Many commercial copiers use an intermediate tray, sometimes called a "duplex" tray for receiving copy sheets that have had one image tranferred to them. The sheets are later fed out of the imtermediate tray to receive a second image as properly controlled by a logic and control unit in the copier. This intermediate tray is used to make duplex copies and to make color copies. In the case of duplex copies, the opposite sides of the sheet receive the images, whereas with two-color copies the same side of the sheet receives two images. Duplex two-color copies can be made by feeding the sheet through the intermediate tray three times.
Sheets fed out of the intermediate tray are generally fed from the bottom. Feeding from the bottom is a difficult task. As a result vacuum rollers have been used for that purpose because of their reliability. However, vacuum rollers are expensive in both power and equipment and may increase the noise output of the machine. Scuff feeding devices are quieter and less expensive but have a tendency to be less reliable. In addition, the freshly fused image on the top of the sheet being fed can be damaged by a scuff pad or scuff roller.
The intermediate tray when used for both duplex and accent color may have sheets in it with images on either the bottom or the top side or both. These images are freshly fused powder images that are more easily disturbed immediately after exiting the fuser than they would be later. It is important that the separating process not disturb these images. It is also important that it not in any way damage the sheet because the sheet and must receive at least one more powder images and must support that image through fusing. Fusing performance is adversely affected by any irregularlity in the sheet.
U.S. Pat. No. 4,844,435 to Giannetti et al issued Jul. 4, 1989 describes a scuff separating device which feeds document sheets from the bottom of the stack using a retard roller which is braked. The brake on the retard roller prevents rotation of the roller when more than one sheet is in the nip but is overcome and permits rotation when one or no sheets are in the nip. This structure is extremely reliable in preventing double feeds and permitting the passage of a single sheet in highly demanding document feeding applications.